The back-grinding machine is a machine to grind the back side of a wafer for obtaining global planarization. The planarization of a wafer back has a great influence on the yield of wafer; a wafer usually includes a front side and a back side; if the back side is not planarized, a wafer can not achieve global planarization even though the front side has been planarized. The yield of wafer is reduced because the back side is not planarized. For this reason, it is necessary for the grind of the back side of a wafer in semi-conductor manufacturing process.
Referring to FIG. 1, it shows a height gauge device 1 of a conventional back-grinding machine, which is used to gauge the height of a wafer 2 so as to have the consumption of the wafer, limited within an extent upon the wafer back 21 being ground with the back-grinding machine. The back-grinding machine includes a cooling water pipe 3 for supplying cooling water to the height gauge device 1 during grinding operation. The height gauge device 1 is mounted under the cooling water pipe 3, and the device comprises a height gauge box 12, a measuring rod 14, a L-shaped linking rod 16, a cylinder 18 and a spring 19.
The height gauge box 12 is substantially a container, which is filled with an oil substance 4 and a signal sensor 123.
The measuring rod 14 includes a measuring end 141, a fulcrum 142 and a sensing end 143; the measuring end 141 is in contact with the signal sensor 123 of the height gauge box 12; the fulcrum 142 is mounted inside the height gauge box 12. The measuring end 141 extends out of the height gauge box 12. The measuring rod 14 is connected with the height gauge box 12 by means of a spring 19.
The L-shaped linking rod 16 includes a first end 161, a second end 162 and an elbow portion 163; the first end 161 is connected with the measuring end 141 of the measuring rod 14; the second end 162 is mounted with a probing needle 164.
The cylinder 18 is mounted under the height gauge box 12, and the first front thereof has a pushing bar 181, which is opposite to the elbow portion 163 of the L-shaped linking rod 16.
The operation procedures of the conventional method to gauge the height of a wafer 2 are as follows
(a) To let the pushing bar 181 on the cylinder 18 push the elbow portion 163 of the L-shaped linking rod 16 so as to have the probing needle 164 on the second end 162 of the rod 16 raised (as shown in FIG. 2). PA1 (b) Put a wafer 2 under the probing needle 164 and then remove the pushing force of the pushing bar 181. PA1 (c) By means of the resilience of the spring 19 between the height gauge box 12 and the measuring rod 14, the probing needle 164 will move downwards to contact with the wafer 2. PA1 (d) During the wafer back 21 being ground with the back-grinding machine, the probing needle 164 of the height gauge device will sense the height variation of the wafer 2; through the L-shaped linking rod 16 and the measuring rod 14, the signal sensor 123 inside the height gauge box 12 will generate a corresponding and varied signal, which will measure and calculate the height of the wafer 2.
However, the spring 19 between the height gauge box 12 and the measuring rod 14 is subject to elastic fatigue or break after the height gauge device 1 being operated for a given period of time. The function of the spring 19 is that as soon as the pushing force of the pushing bar 181 on the cylinder 18 is removed, the probing needle 164 will press down on the wafer 2. In the event of the probing needle 164 moving down too slowly or unable to move down, the operation of the back-grinding machine will be interrupted; in that case, the spring 19 suffered from elastic fatigue or break must be replaced.
When the spring 19 in the conventional height gauge device 1 is replaced, the height gauge box 12 must be opened first; unfortunately, once the height gauge box 12 is opened, the oil substause 4 therein would leak out or be polluted. The quantity and purity of the oil substanse 4 in the height gauge box 12 will definitely affect the accuracy of the height gauge device 1; in other words, after the spring 19 in the height gague box 12 is replaced, the measuring result of the wafer 2 would have a tolerance more or less. In that case, the whole height gauge device 1 must be replaced, and then more money and time will cost.